Design of Supports for Vertical Vessels

There will be no stress from intemal or external pressure for the skirt, unlike for the shell of the vessel, but the stresses from dead weight and from the wind or seismic bending moments will he a maximum. The same procedure may be us i- for designing the skirt as for designing the shell, which was described in Chapter 9. Note Subscript b refers to the base of the skirt. 

After the skirt and bearing plate have been designed, the skirt design should be cheeked for the rt action of the bolting chairs or ring. (See sefrtipn 10.1 g.) 

1b Skirt-bearing plote and Andior boit Design. The bottom of the skirt of the vessel must securely anchored to the concrete foundation by means of anchor bolts embedded in the concrete to prevent overturning from the bending moments inducted by wind or seismic loads. 

The concrete foundation is poured with adequate reinforcing steel to carry tensile loads (143, 154, 155). Fhe anchor bolts may be formed from steel rounds threaded t one end and usually with a curved or hooked end embedded in, the concrete. The boltii material should be clean and free of oil so tiiat the cement in the concrete will bond to the eiiibedcieKl surface of the steel.  

Wiien eil - a compressive or tm e load i apphed the anchor bolls, the loud is transferred from the steel through the bund to the concrete. Surface irregularities, bends, and hooks aid in transferring loads from steel to concrete. As the steel and concrete are bonded, the resulting strain is the same for both the steel and concrete at the bond. The modulus of elasticity of steel. Eg, is about 30 X 10 psi while that of concrete, Ec, varies from about 2 X 10 to 4 X 10 j i depending upon the mix employed. The ratio of these moduli is  

---

Design of Supports for Vertical Vessels butrfr = Iherefote... 

External-Cake Tubular Filters Several filter designs are available with vertical tubes supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel (Fig. 18-115). The tubes may be made of wire cloth porous ceramic, carbon, plastic, or metal or closely wound wire. The tubes may have a filter cloth on the outside. Frequently a filter-aid precoat will be applied to the tubes. The prefilt slurry is fed near the bottom of the vertical vessel. The filtrate passes from the outside to the inside of the tubes and into a filtrate chamber at the top or the bottom of the vessel. The sohds form a cake on the outside ofthe tubes with the filter area actually increasing as the cake builds up, partially compensating for the increased flow resistance of the thicker cake. The filtration cycle continues until the differential pressure reaches a specified level, or until about 25 mm (1 in) of cake thickness is obtainea... 

Cladding for the reactor vessel is a continuous integral surface of corrosion-resistant material, having -inch (0.56 centimeter) nominal thickness, and a f-inch minimum thickness. The reactor vessel is supported by four vertical columns located under the vessel inlet nozzles. These columns are designed to flex in the direction of horizontal thermal expansion and thus allow unrestrained heat-up and cool-down. The columns also act as a hold-down device for the vessel. The supports are designed to accept normal loads and seismic and pipe rupture accident loads. 

The method used to support a vessel will depend on the size, shape, and weight of the vessel the design temperature and pressure the vessel location and arrangement and the internal and external fittings and attachments. Horizontal vessels are usually mounted on two saddle supports see Figure 13.20. Skirt supports are used for tall, vertical columns see Figure 13.21. Brackets, or lugs, are used for all types of vessels ... 

These vessels are usually constructed of steel or alloy steel and are almost always designed to be self-supporting. This requirement for self-support introduces special design considerations for tall vertical vessels, particularly when the vessels are exposed to high velocity winds and to seismic vibrations. 

One of the most common methods of supporting vertical pressure vessels is by means of a rolled cylindrical or conical shell called a skirt. The skirt can be either lap-, fillet-, or butt-welded directly to the vessel. This method of support is attractive from the designer s standpoint because it minimizes the local stresses at the point of attachment, and the direct load is uniformly distributed over the entire circumference. The use of conical skirts is more expensive from a fabrication standpoint, and unnecessary for most design situations. 

The reactor vessel is supported by four vertical columns located under the vessel inlet nozzles. These columns are designed to flex in the direction of horizontal thermal expansion and thus allow unrestrained heatup and cooldown. They also act as holddown devices for the vessel. 

Design a skirt support for a pressure vessel with a total vertical load of 720 kN, and an overturning moment of 2050 kNm. The bolt circle diameter of the support may be assumed to be 4.5 m. Assume a thickness of 10 mm for the support skirt and the mean diameter of the support as 4.25 m. 

Rolled-anole Beahimg Plate. If the vertical vessel is not very high and a skirt is used to support the vessel rather than le, lugs, or columns, a simple design may suffice for the bearing plate. If the calculated thickness of the bearing plate is in. or less, a st l angle rolled to lit the outside of the skirt may he lap welded as shown in Fig. 10.3. 

---